Injection-level dependent recombination lifetime measurements of iron-diffused, boron-doped silicon wafers of different resistivities are used to determine the electron and hole capture cross sections of the acceptor level of iron–boron pairs in silicon. The relative populations of iron–boron pairs and interstitial iron were varied by exposing the samples to different levels of illumination prior to lifetime measurements. The components of the effective lifetime due to interstitial iron and iron–boron pairs were then modeled with Shockley–Read–Hall statistics. By forcing the sum of the modeled iron–boron and interstitial iron concentrations to equal the implanted iron dose, in conjunction with the strong dependence of the shape of the lifetime curves on dopant density, the electron and hole capture cross sections of the acceptor level of iron–boron pairs have been determined as and

Exchange coupling between antiferromagnetic regions of tetragonal NiMn through a separation at a boundary was evaluated by first principles calculation to study the coupling between antiferromagnetic grains. It was assumed that the crystallographic orientation was assumed not to change across the boundary. The layer version of the Korringa–Kohn–Rostoker method was employed to calculate the total energy of the coupled system. The exchange coupling strength was estimated as the total energy difference between the two spin configurations of the two body system, parallel and antiparallel to each other. For the grains without any atomic lattice shift parallel to the plane (100) across the boundary, it was found that the coupling strength decreases more rapidly than that for ferromagnetic hexagonal cobalt with the increase of the separation and that it changes its sign at a separation length of a little greater than a half of the lattice constant. For the case with a boundary across which the lattice shifts by an atomic distance diagonally, the exchange coupling is reduced to about 1/3 of the original value and decreases rather slowly with the increase of the separation compared to the previous case. Those results are consistent with our previous report which predicted the existence of a weak exchange coupling between the grains in an antiferromagneticpolycrystalline layer based on the analysis of a characteristic feature often observed in torque curves for ferro/antiferromagnetic coupled layer systems.

Quantum-dot cellular automata (QCA) may offer a viable alternative of traditional transistor-based technology at the nanoscale. When modeling a QCA circuit, the number of degrees of freedom necessary to describe the quantum mechanical state increases exponentially making modeling even modest size cell arrays difficult. The intercellular Hartree approximation largely reduces the number of state variables and still gives good results especially when the system remains near ground state. This suggests that a large part of the correlation degrees of freedom are not essential from the point of view of the dynamics. In certain cases, however, such as, for example, the majority gate with unequal input legs, the Hartree approximation gives qualitatively wrong results. An intermediate model is constructed between the Hartree approximation and the exact model, based on the coherence vector formalism. By including correlation effects to a desired degree, it improves the results of the Hartree method and gives the approximate dynamics of the correlation terms. It also models the majority gate correctly. Beside QCA cell arrays, our findings are valid for Ising spin chains in transverse magnetic field, and can be straightforwardly generalized for coupled two-level systems with a more complicated Hamiltonian.

Carbonthin films were grown by magnetron sputtering at room temperature on silicon substrates, with the substrate bias voltage varying from +10 to −200 V. Transmission electron microscopy analysis has shown that filmsdeposited at and −40 V are amorphous (α-C), while filmsdeposited at V are nanocrystalline (nc-C). Temperature dependent conductivitymeasurements were carried out in the temperature range 300–77 K. With respect to conductivity, the results indicate that the investigated carbonfilms are classified in three groups: (i) In α-C filmsdeposited at V rich bonds), the variable range hopping (VRH) conduction dominates below 300 K. (ii) In α-C filmsdeposited at negative up to −100 V rich bonds), VRH conduction dominates at low temperatures K) and a thermally activated process satisfying the Meyer–Neldel rule at higher temperatures K). (iii) In nc-C filmdeposited at V, the conductivity is explained by a heteroquantum-dots model based on a thermal-assisted tunneling process. The earlier differentiation in the conductivity mechanisms may play a significant role in the field electron emission properties of the films.

Comprehensive studies of the electrical properties of Mg-doped bulk GaN crystals, grown by high-pressure synthesis, were performed as a function of temperature up to 750 °C. Annealing of the samples in nitrogen ambient modifies qualitatively their resistivity values ρ and the variation. It was found that our material is characterized by a high concentration of oxygen-related donors and that the charge transport in the studied samples is determined by two types of states, one of shallow character (Mg-related state, and the second one much more deep, (above the valence band). Depending on the effective concentration of either states, different resistivities ρ can be observed: lower resistivity at ambient temperature) in samples with dominant states and very high resistivity at ambient temperature) in samples with dominant states. For the first type of samples, annealing at leads to a decrease of their resistivity and is associated with an increase of the effective concentration of the shallow Mg acceptors. Annealing of both types of samples at temperatures between 600 and 750 °C leads to an increase of the deep state concentration. The presence of hydrogen ambient during annealing of the low-resistivity samples strongly influences their properties. The increase of the sample resistivity and an appearance of a local vibrational mode of hydrogen at 3125 cm−1 were observed. These effects can be removed by annealing in hydrogen-free ambient.

The evolution of GaN luminescence under electron beam injection has been studied by means of in situcathodoluminescence experiments on various epitaxial lateral overgrown samples. It is shown that the ultraviolet (UV) peak of undoped materials experiences a decrease of its intensity as well as a noticeable redshift, while the other extrinsic peaks only experience an intensity decrease. However, in Mgdoped materials the UV peak intensity decrease is followed by an increase of its intensity which can even reach larger values than the initial one. We suggest that all these features are self-consistently explained by the occurrence of strain relaxation resulting from the beam enhanced diffusion of vacancies from the free surface, and from the coalescence boundaries towards the bulk.

We have calculated the crystal-field splitting of the energy levels of in GaN and have compared these results to an analysis reported recently of the photoluminescence and the cathodoluminescence spectra of implanted in GaN by metal organic chemical vapor deposition on sapphire substrates. The lattice location of Pr in GaN determined recently by the emission channeling technique, provides direct evidence that substitutional Ga sites are thermally stable lattice positions for Pr. The lattice-sum calculations with Pr occupying Ga sites include effective ionic charges, multipole polarizabilities, and structural information also available in the literature. From the calculations, we conclude that the majority of the reported emission spectra is associated with ions in a common site with transitions from excited and states to crystal-field split multiplets, (the ground state), and

We report optical studies on alloy layers across the full composition range. The series of alloy layers was grown on (111)-oriented silicon substrates using gas-source molecular beam epitaxy. From reflectance measurements, we determine the composition dependence of the energy gap to be in good agreement with previous work. By combining Fourier transform infrared and Raman spectroscopy studies, we determine the composition dependence of phonons having and symmetry. The longitudinal optic phonons exhibit one-mode alloy behavior. Two-mode alloy behavior is observed for all transverse optic and the phonons (i.e., each mode has AlN-like and GaN-like branches). All phonons are seen to blueshift with increasing x. The influence of stress on the phonon energies is discussed.

GoldSchottky contacts to n-AlGaN were fabricated, and the influence of the semiconductor surface preparation on the electrical performance of the diodes was examined. More significantly, the electrical characteristics of the diodes were found to be sensitive to the environment in which they were exposed. Diodes stored in vacuum had stable but poor electrical characteristics, exhibiting the same high reverse leakage currents, low barrier heights, and high ideality factors as the freshly prepared diodes. On the other hand, didoes exposed to air changed over the course of days, in some cases with decreases in the reverse leakage currents by four or more orders of magnitude and increases in the barrier height by 0.3–0.5 eV. Further study of this change in electrical properties showed that the effect was reversible with exposure to gas or vacuum and adequate temperature. In addition, the effect was more pronounced when the metal contact was thin, indicating that diffusion of gases through the metal was significant. This study suggests that nitride semiconductor devices with Schottky barriers to n-AlGaN as components may exhibit improved performance if they are initially stored in air for a few days prior to encapsulation and will also exhibit a pronounced sensitivity to their storage and operational environment if not adequately protected from it.

A layer-Korringa–Kohn–Rostoker calculation is used to study the compositional dependence of the surfaceresistivity of the (111) surface of alloys. The compositional disorder in the bulk and at the surface is described by the coherent potential approximation. If it is assumed that the atomic planes near the (111) surface have the same composition as the bulk layers, then a weak Nordheim effect is observed in the compositional dependence of the surfaceresistivity. However, we show that surface segregation in causes an inverse Nordheim dependence in the actual surfaceresistivity as the bulk composition is varied.

Fowler–Nordheim current in Si-poly structures, with an oxide thickness varying between 3 and 12 nm, has been measured and numerically computed with the exact electric field in the oxide, the field dependence of the barrier shape with the image force, and the temperature effects. The fit of the experimental data leads to an accurate determination of the electron affinity difference and the barrier height at the emitting Si–poly -gate-electrode–oxide interface. The evolution of these two parameters with temperature is discussed in relation with the oxide thickness.

The influence of electron scattering by rough boundaries on electrical conductivity of quantum wires is studied in the diffuse transport limit within the kinetic Boltzmann equation approach. The considerations are restricted to the wires obtained by lateral confinement of a two-dimensional electron gas. Both intra- and interboundary roughness correlations are taken into account. It is shown that the cross correlations usually increase the conductivity, leaving the shape and phase of the quantum size oscillations almost unaffected.

In this article, we give an overview of the domain duplication process which can occur in ferromagnetic sandwiches. A brief theoretical description of the process allows us to extract the main parameters governing the effect. It is shown that even if a domain structure exists in the hard electrode, no duplication can occur for a ferromagnetic coupling below a minimum value. Then, we address also the effects of residual domains on the nucleation field of the hard electrode to reconcile theory and experiments.

The thermal stress effects of the inter-level dielectric (ILD) layer on the ferroelectric performance of integrated capacitors were investigated. Two different thin film materials, pure grown at 650 °C and B- and P-doped grown at 400 °C by chemical vapor deposition techniques, were tested as an ILD layer. The ILD layer encapsulated the SBT capacitor array. During high temperature thermal cycling (up to 800 °C) after ILD deposition, which is used for both densifying the ILD and curing of the various damage imposed on the SBT capacitors, a large thermal stress occurred in the bottom Pt layer due to the thermal expansion mismatch between the various layers. In particular, the pure ILD layer between the capacitors did not allow thermal expansion of the Pt layers, which led to a large accumulation of compressive stress in the layer. This resulted in hillock formation in the bottom Pt layer and eventual capacitor failure. However, the B- and P-doped ILD layer contracted during thermal cycling by removing residual impurities, which allowed greater expansion of the Pt layer. Therefore, compressive stress accumulation did not occur and excellent ferroelectric properties were thus obtained from the integrated capacitor array.

Amounts of spontaneous spin splittings were estimated from low-temperature magnetoresistances in two-dimensional electron gases created at heterojunctions under a gate bias. Typical sheet electron densities and mobilities in the raw wafers were and at 1.5 K, respectively. A maximum spin-orbit coupling constant of was obtained for the van der Pauw sample. In gated Hall-bar samples, a decrease in the value with decreasing gate voltage was first confirmed in a normal heterojunction. The main origin for such a large which is a few times larger than any previously reported, was found to be a structure-dependent so-called interface contribution in the Rashba term.

a wide band gap semiconductor with the delafossite structure, has been synthesized in bulk and thin-film form. Bulk undoped is almost black and has moderate conductivity with p-type carriers. Upon doping with 5% Mg, the conductivity increases by a factor of 1000. In films, the best p-type conductivity is 220 in a factor of 7 higher than previously reported for Cu-based p-type delafossites. Undoped films have a conductivity of order 1 Films are usually polycrystalline on amorphous substrates, but undoped films can be c-axis oriented if deposited at or above 650 °C. Optical and ultraviolet transmission data indicate a direct band gap of 3.1 eV.